As shown in the bottom plan view of FIG. 6, a small watercraft of the prior art has a hull 50 on whose bottom surface there is provided a plurality of longitudinal chines 51 protruding from the hull bottom surface and extending in a longitudinal direction from the aft toward the fore part of the hull 50. A plurality of backwardly curved transverse chines 52 also protrude from the hull bottom surface and extend in transverse directions at the fore part of the hull 50, and are formed in a smoothly continuous fashion from the respective longitudinal chines 51 (see Japanese Patent Provisional Publication No. 62-34897).
The protruding longitudinal chines 51 prevent the hull 50 from sliding sideways when planing across water, and thereby improves its course stability. On the other hand, the protruding transverse chines 52 prevent the water through which the hull 50 is thrusting from being scattered forward and splashed on the occupants of the craft. Furthermore, when the hull 50 is subjected to a pitching motion, the transverse chines 52 accept the lift from the water and cause the bow to rise, thereby improving the speed performance.
However, when forming the stripes 51 and 52 in continuous fashion as described above, the transverse ends of each transverse chine 52 need to be smoothly bent backwardly through a large angle. This large angle bend inevitably requires that the junction points 53 between the transverse and the longitudinal chines must be positioned toward the aft part of the hull, with the result that most of the straight portions of the longitudinal chines 51 are located in the aft part.
This reduces the length of the longitudinal chines 51, and hence degrades the course stability of the hull 50. In particular, when the watercraft is turning, a portion of the protruding transverse chines 52 (in most cases, the rearward portion) touches the water, and with this portion acting as resistance to the water, an excessive force is exerted which acts to further turn the watercraft in that direction, and thus good course stability cannot be obtained. Furthermore, when the waves are high, the rearward portion of the transverse chines 52 tends to touch the water even when the craft is moving straight forward, and the resistance to the water thus increases.
Moreover, as shown in FIG. 7, which is an elevational view of the prior art watercraft of FIG. 6, each transverse chine 52 has a protruding edge 54 whose front face 55 is substantially vertical to the water surface. As a result, when the wave strikes this front face 55, a large resistance is produced.
The present invention has been devised in view of the above problems, and it is therefore desired to provide a hull shape of a small watercraft that is effective in preventing the water through which the craft is moving from being splashed on the occupants of the craft, and that can enhance the course keeping ability of the hull, especially when turning, while at the same time, reducing the resistance of the hull to the water.
It is also desired to provide a hull shape of a small watercraft which does not produce large resistance even if waves strike the protruding transverse chines from the forward direction.